1. Field of the Invention
This invention relates to a display device comprising three fluorescent color layers, i.e. red, blue and green layers, on the inner surface of the display panel thereof.
2. Description of the Related Art
In recent years, there have been proposed various methods for improving the contrast of display devices such as a color cathode-ray tube, etc. For example, JP Laid-open Patent Publications (Kokai) No. 6-275209 (1994) and No. 10-112266 (1998) disclose a method for improving the contrast of display devices wherein the surface of particles of a red fluorescent substance is coated with a red pigment and likewise, the surface of particles of a blue fluorescent substance is coated with a blue pigment.
There is also disclosed, for example in JP Patent Publications No. 52-14587 (1977), JP Laid-open Patent Publications (Kokai) No. 9-27284 (1997) and No. 11-204056 (1999), a method for improving the contrast of display devices, wherein a color filter is interposed between the phosphorous layer and the face plate of display device.
However, the aforementioned method of covering the surface of particles of fluorescent substance with a pigment of the same color as that of the fluorescent substance is accompanied with the problem that since the emission of fluorescent substance is caused to be absorbed by the pigment, degrading the brightness of the display device, it is imperative to limit the quantity of pigment to be adhered to the fluorescent particles. As a result, it is impossible to sufficiently improve the contrast of display devices.
Further, although the aforementioned method of interposing a color filter between the phosphorous layer and the face plate of display device is effective in improving the contrast of display device, there are problems that the manufacturing process is very complicated and hence there are many difficulties in the manufacture of the display device, thus inviting an increase in manufacturing cost.
There is also known a method which is directed to improve the color purity and emission brightness of a red fluorescent substance, this object being realized by increasing the concentration of Eu in a red fluorescent substance (see for example, JP Laid-open Patent Publications (Kokai) No. 6-52807 (1994)). This method however is accompanied with a problem that since a large amount of Eu which is expensive is required to be employed, the manufacturing cost of display device would be increased.
The present invention has been accomplished in view of the aforementioned problems and hence one of the objects of the present invention is to provide a display device which is improved in the contrast thereof while making it possible, while making use of the same manufacturing process as conventionally employed, to maintain the luminance brightness of the display device.